1. Field of the Invention
This invention relates to the field of mining and material handling, and in particular to a chute for conveying mining materials.
2. Description of Related Art
From high rises to highways, drainage pipes to railroad beds, houses to hospitals, the aggregate, cement, concrete and mining material industries provide the glue and buildings blocks of modern life. For example, we use them to build our schools and commercial buildings because concrete and aggregate products will not burn. Also, water purification systems are made from concrete products because they are clean and easy to maintain. At the same time, these products are natural and reusable. Sand, crushed stone, gravel, cement, and water in all of their combinations and forms are natural resources and part of the earth. Low in cost, natural aggregates are a major contributor to and an indicator of the economic well being of a nation.
It is important to note that more than three billion tons of aggregate were produced in the United States (U.S.) in 2004 with a value of approximately $16 billion, contributing $37.5 billion to the U.S. Gross Domestic Product. Every $1 million in aggregate sales creates 19.5 jobs, and every dollar of industry output returns $1.58 to the economy. Also, about ten tons of aggregate per person are used annually in the U.S. Every mile of interstate highway uses 38,000 tons of aggregate and about 400 tons of aggregate is used to build the average home.
Mining materials also have an amazing variety of other uses. Imagine our lives without wallboard and roofing tiles or without paint, glass, plastics, and medicine. When ground into powder, limestone is used as an important mineral supplement in agriculture, medicine and household products. Mining materials are also being used more and more to protect our environment. Soil erosion-control programs, water purification, and reduction of sulfur dioxide emissions generated by electric power plants are just a few examples of such uses.
Even after these materials are extracted and utilized, the job still is not finished. For example, what was once the bottom of a rock quarry can become a golf course, school, theme park or shopping center. Furthermore, these natural mining materials are a major basic raw material used by construction, agriculture, and industries. Mining industries employ complex chemical and metallurgical processes.
Carefully managing these valuable and limited resources is essential for the environment, economy, and future of a nation. For this reason, mining material producers, industry service providers and equipment suppliers are continually procuring ideas and innovations to help with the industry.
The mining industry utilizes a variety of methods to excavate such natural resources. These methods are dependent upon the geologic characteristics of the natural deposit. Open-pit mining and quarrying are commonly used. Other deposits require mining underground. Sand and gravel deposits above the water table are excavated with bulldozers, front-end loaders, tractor scrapers, and draglines. Deposits below the water table, including stream and lakebed deposits, may be excavated with draglines or from barges using hydraulic or ladder dredges. Mining and quarrying stone generally require drilling and blasting, after which the rock is then transported to a processing facility on trucks and conveyors.
Processing plants are generally constructed on the site of extraction. Processing of mined or quarried rock requires primary and possible secondary crushing, depending on the sizes of mining material needed. After crushing, the crushed stone, sand and gravel usually are sorted to size, moved by conveyors to bins or stockpiled.
Chutes associated with these processing steps are subjected to a great deal of wear and tear, not only by the impact and abrasion resulting from movement of the ore and other fluent material but also by the impact of other machinery or equipment. Impact and wear of the chutes will, over a period of time, result in significant deterioration. Another contributing factor to such deterioration is exposure of the chutes to the liquid components of mining materials.
One approach has been to weld liners of steel to the chutes. This is an expensive procedure requiring significant labor and hoisting machinery. Furthermore, chutes in a significant state of deterioration or chutes of certain types of materials are often not amenable to repair utilizing this approach. Use of steel or other metal liners also adds significant weight to the chute, which is undesirable.
Attempts have been made to coat chutes with plastic or elastomer materials; that is, a bond is created between the plastic and the chute material over the entire extent. This causes difficulties due to the difference in coefficients of expansion of the two materials. Furthermore, any break in the coating will result in the underlying chute material coming into contact with liquid or other types of processing materials, thus causing corrosive or abrasive wear that will over time significantly deteriorate the quality and strength of the chute. This same result can, of course, occur even when steel liners or plates are affixed to chutes. And it almost goes without saying that the various attempts to protect in these processing plant chutes result in permanent alteration of the chutes. That is, the various liners and coatings become integral parts of the chutes, rendering further repair even more difficult, if not impossible.
U.S. Pat. No. 5,035,313, “Telescopic chute for a mixer truck,” issued Jul. 30, 1991 to Smith discloses a dispensing chute for attachment to a mixer truck comprising a plurality of telescopically mounted sections. The chute sections are in the form of interlocking open top curved metal sections having replaceable plastic liners affixed to interior portions of the metal sections.
U.S. Pat. No. 4,054,194 “Discharge chute for concrete mix,” issued Oct. 18, 1977 to Davis discloses a conveying chute for freshly mixed concrete made with cross members at each end of the chute connected by two outer longitudinal members on opposite sides of the chute. It also has a bottom member between the cross members along the bottom of the chute. The chute includes a metal mesh reinforced polyurethane liner fastened to the cross members at each end of the chute by sets of bolts and nuts.
Existing concrete chutes used with aggregate transport vehicles or with stationary processing mining material and mixing plants, are typically made of steel with and without reinforcing members. Such chutes are heavy and difficult to manipulate. Also, chutes associated with aggregate transport are subject to a great deal of wear and tear not only by the impact and abrasion resulting from the movement of the aggregate or other fluent materials, but also by the impact of other machinery and equipment. In response to such conditions, chutes have been developed that have a liner attached in the chute to ameliorate the abrasion and impact conditions experienced by the chute during their use.
These devices typically will bolt or otherwise fasten the liner to the chute in order to maintain the liner within the chute throughout the chute's operational positions. Problems continue to exist; however, in that the fasteners wear as the ore moves over the fasteners, and the fasteners are subject to corrosion and rust either from the ores' chemical composition or from the process fluids.
Other liners have been laminated to the chute in order to avoid the wear and corrosion of hardware described above. However, the laminated liners, experience different thermal expansion characteristics which causes stress and cracks that allows aggregate and other fluent materials to attack the chute. Also, laminated liners cannot be easily replaced or repaired and typically a new chute is required. Other chutes composed of materials other than metal and with or without liners have also been used. However, such chutes are not as resilient to the conditions they are exposed to and further cracking and breaking requires replacement of the entire chute.
A need exists for a lightweight but strong chute for use with processing plants in the mining material industry. Elastomers such as rubber and urethane are better suited than other plastics, metals, or other materials, because of their resistance to abrasion, elasticity, and because of their relatively low weight. Urethane is also of special interest due to its particularly smooth surface. U.S. Pat. No. 4,362,231, “Chute for Transporting Timber,” issued Dec. 7, 1982 to Meyer utilizes polyurethane material to construct the chute.
The present invention provides a solution to these needs and other problems, and offers other advantages over the prior art.